1 . Field of the Invention
The present invention relates to a safety pneumatic tire, in particular, a safety pneumatic tire (tire assembly) which is greatly improved in both run-flat durability and riding comfort characteristic. More particularly, the present invention is concerned with a safety pneumatic tire which is equipped with a side-reinforcing layer and is filled with specific elastic foam in the internal hollow portion encompassed by a tire shell and a rim.
2. Description of the Related Arts
A number of proposals for a safety pneumatic tire have heretofore been made in order to enable the tire to continue running for the time being even in the case where the tire is deprived of pneumatic pressure by reason of puncture, flattening or the like. For instance, there is known a pneumatic tire which comprises a tire shell and closed cell-based foam which is filled into the internal hollow portion of the assembly composed of the tire shell and a rim which fits the above-mentioned tire to itself (refer to Japanese Patent Application Laid-Open Nos. 127207/1994(Hei-6), 183226/1994(Hei-6), 186610/1995(Hei-7), 332805/1996(Hei-8) and the like.
However, any of the tires disclosed therein is limited mainly to a special tire or a small-sized tire such as a tire for agricultural or tillage use, a rally tire, a tire for a two-wheeled vehicle, a bicycle tire and the like. In addition, there have heretofore been proposed a variety of safety pneumatic tires such as a tire of double-wall structure, a tire equipped inside with a load-supporting apparatus, and a side-reinforced tire. Of these, an example of the most general tire in practical service at the present time, is so-called a side-reinforced tire which is equipped with a side-reinforcing layer composed of relatively hard rubber lying inside of the side wall portion and extending over both the shoulder portion and the bead portion . Such kind of tire is used principally for a run-flat tire having an aspect ratio of at most 60%. Moreover, in the case of a pneumatic tire having a relatively large height and an aspect ratio of at least 60% , there is known a run-flat tire with such a structure that supports the load at the time of puncture or flattening by mainly fixing a tire-supporting member into a rim in order to avoid the heat build-up in the side wall portion due to relatively long-distance running with a high speed.
On the other hand, the requirements For the performance of a run-flat tire tend to be more and more enhanced, and thus it is the actual situation that further improvement in a possible run-flat distance of the tire is eagerly desired. In particular, in the case of a safety pneumatic tire with an aspect ratio of at least 60% , the tire is desired to exhibit satisfactory riding comfort characteristic under normal condition as well as sufficient run-flat durability. However, the problems in conventional side-reinforced tires still remain unsolved in that the run-flat durability is improved to some extent, but is not yet sufficiently improved, the riding comfort characteristic and the rolling resistance are markedly worsened, and in addition the tire weight is unfavorably increased.